Compression braking is known in the art and is used for many applications, including braking heavy vehicles. Compression brakes convert an internal combustion engine cylinder to a compressor by cutting off the fuel flow and opening an exhaust valve of the cylinder near the end of the compression stroke. This allows the power generated in the piston to escape to the atmosphere, rather than continuing to power the vehicle. One type of compression braking system is shown in U.S. Pat. No. 6,253,730 to Gustafson.
An early technique for accomplishing compression braking is disclosed in U.S. Pat. No. 3,220,392 to Cummins, where a slave hydraulic piston located over an exhaust valve opens the exhaust valve near the end of the compression stroke of an engine piston with which the exhaust valve is associated. To place the engine into braking mode, solenoids are energized which cause pressurized lubricating oil to flow through a control valve, creating a hydraulic link between a master piston and a slave piston. The master piston is displaced inward by an engine element (such as a camshaft mechanism) periodically in timed relationship with the compression stroke of the engine. A typical modern compression braking system may include exhaust valves operated during the engine's power mode by an exhaust rocker lever.
The system may also include a reset valve which operates to cause the slave piston to retract after an initial opening of the exhaust valve during braking. As a result, the exhaust valve is closed prior to the end of the expansion stroke and before the hydraulic pressure drops due to a return motion of the master piston. This design advantageously avoids shock or asymmetric loading of the valve or valve crosshead by the exhaust rocker arm at the start of the main opening event of the exhaust valve following the initial opening event.
The modern compression braking system has been further improved by the system disclosed in Gustafson, wherein the engine compression braking system has an integral rocker lever and reset valve capable of effectively avoiding asymmetric loading of a valve crosshead while providing accurate and predictable compression braking. However, further improvements in this technological area are desired.